Method of making composite wire mesh seal

ABSTRACT

A high temperature seal, particularly suitable for use in vehicle engine exhaust systems, is formed of a composite structure including refractory sheet material and wire mesh. In a typical application, the seal is disposed between confronting ends of an engine exhaust manifold pipe and an exhaust tail pipe, and permits relative rotation of the pipes without impairment of the effectiveness of the seal, thereby preventing leakage of high temperature exhaust gases passing through the joined pipes.

This invention relates generally to high temperature exhausts seals and,more particularly, to a composite seal including flexible refractorysheet material and wire mesh, the seal being especially useful invehicle exhaust systems.

There are two general approaches to mounting a vehicle engine. In oneapproach, the engine is mounted so that its crankshaft runslongitudinally with respect to the vehicle body (hereinafter referred toas a longitudinally mounted engine). In the other approach, the engineis mounted so that its crankshaft runs transversely with respect to thevehicle body (hereinafter referred to as a transversely mounted engine).The latter arrangement is particularly useful for front wheel drivenvehicles.

With regard to the exhaust systems appurtenant to these engines, it willbe apparent that a particular exhaust system, which includes an engineexhaust manifold and tail pipe, will vary in its configuration dependingupon the engine mounting orientation with respect to the vehicle, i.e.,longitudinal or transverse.

For example, in the case of a longitudinally mounted engine, or exhaustmanifold pipe extends from the engine exhaust manifold down alongside ofthe engine, and usually has a flange joined at its opened end whichfaces downward for connection to a mating flange on a tail pipe runningbeneath the vehicle. With this configuration, a seal is usually disposedbetween the connected flanges for preventing exhaust gas leakage outaround the joined flanges. Movement of the exhaust manifold, such ascaused by normal operation of the engine, is fully communicated to thetail pipe by way of the joined flanges. Stresses caused by the tail pipemovement are absorbed by flexible mountings (also known as hangers)which secure the tail pipe to the underside of the vehicle body. Thetypical exhaust seals therefore need not absorb any of these stressesand, because of this, they are of relatively simple construction. Atypical seal used in longitudinally mounted engine applications is madeof cast iron, and has tapered bearing surfaces which cooperate with thesurfaces of the flanges to effect a tight seal. Other seals for theseapplications employ a laminate construction including asbestos andperforated sheet steel. Still other conventional seals may includeimpregnated asbestos yarn knitted within a wire mesh, these materialsbeing pressed together to form the seal. In some instances, no seal isused at all, the flanges themselves effecting a sealed joint whenconnected together.

Transversely mounted engines, however, present a more difficult problem.Usually, the exhaust manifold pipe extends downward alongside the engineand has a flange at its opened end which also faces generally downward.However, normal engine operating movement resulting from rotationalmomentum of the crankshaft and opposing torsional forces of thedriveshaft causes the exhaust manifold pipe flange to reciprocate insuch a manner that the central axis of the pipe, which is perpendicularto the plane of the flange, departs from a substantially vertical lineand becomes inclined alternately towards the front and rear of thevehicle. It is necessary to use a flexible joint between the exhaustmanifold and the tail pipe to absorb this movement; otherwise it will becommunicated directly to the tail pipe causing intolerable stresses andstrains. Such stresses and strains can cause metal fatigue andaccelerate failure of the tail pipe. Excessive noise can also begenerated by vibrations induced by the stress reversals.

It will therefore be understood that with a transversely mounted engine,the exhaust seal in the flexible joint must be capable of permitting adegree of relative rotation between the exhaust manifold and tail pipesand still maintain an effective exhaust gas seal. Exhaust seals whichare useful with longitudinally mounted engines are undesirable for usein vehicles having transversely mounted engines, because they cannotwithstand the relative rotative movement and stress encountered in theflexible exhaust joints used with the latter. An attempt to overcomethis problem has been to include a section of corrugated pipe betweenthe exhaust manifold and the tail pipe in the hopes that the corrugatedsection could absorb the relative rotative movement and stressesproduced therebetween. In practice, this solution has not provedsuccessful since the corrugated pipe frequently fractures as a result ofmechanical fatigue under high temperature operating conditions.

Another solution to overcome the problem of providing a sealed exhaustjoint which tolerates some relative pipe movement is a "ball and socket"type joint such as, for example, that shown in U.S. Pat. No. 3,188,115,issued June 8, 1965. The joint disclosed in the patent, however, is notsatisfactory for permitting relative rotative movement of one of thejoined pipes, since bolts which pass through unslotted openings in thejoint pressure plate will cause both pipes to rotate in unison.

Another exhaust seal, for use in a flexible exhaust joint adapted toallow for relative rotative pipe movement, includes graphite sheetmaterial surrounding perforated sheet metal. That seal has provenunsatisfactory in meeting the severe operating requirements of theflexible joint. In particular, the seal lacked structural integrity andunder normal operating stress its composite layers of graphite and sheetmetal would separate from one another causing failure of the seal.

The present invention provides an exhaust seal capable of meeting therigorous operating requirements imposed by a flexible exhaust joint, isparticularly suitable for use in transversely mounted engine exhaustsystems, and can be effectively used therein as well as in many otherapplications which will be suggested to one skilled in the art uponreading of the disclosure herein.

An exhaust seal according to the present invention includes wire meshhaving openings between the wires thereof, and flexible refractory sheetmaterial surrounding the wires and substantially filling the openings inthe wire mesh.

In a preferred embodiment, the present invention provides an exhaustseal formed of flexible refractory material in sheet form which ispressed through the openings of the wire mesh after it is convolutedthereover.

An important advantage of the exhaust seal according to the presentinvention is its unusually high resiliency which makes it particularlysuitable for use in flexible exhaust joints which connect exhaustmanifold and tail pipes together in vehicles having transversely mountedengines. This resiliency allows the seal to absorb a high degree ofrotative stress when positioned within the flexible joint. Additionally,due in part to a relatively high amount of lubricity on its bearingsurface, the present seal permits relative rotative movement of the pipewhich engages its bearing surface, and still maintains an effective sealagainst exhaust gases passing through both of the joined pipes.

The seal of the present invention is preferably produced by constructinga cylindrical preform which includes refractory material in flexiblesheet form and wire mesh, and axially compressing the preform with apredetermined force to thereby form the finished product.

Other advantages and applications for the exhaust seal of the presentinvention will be apparent upon a reading of the following detaileddescription thereof with reference to the accompanying drawings.

In the drawings:

FIG. 1 is a perspective partially broken view of an exhaust sealaccording to the present invention showing the refractory material andwire mesh therein;

FIG. 2 is a side elevational view, fragmented and partially in section,showing the present exhaust seal disposed in operative position betweenan exhaust manifold and tail pipe of an automobile;

FIG. 3 is a view taken along line 3--3 of FIG. 2;

FIG. 4 is a perspective view of a layer of wire mesh and a layer ofrefractory sheet material positioned together prior to forming the sealby a method of the present invention; and,

FIG. 5 is a top view of a preform configuration for the wire mesh andrefractory material of FIG. 4.

Referring now to the drawings, and in detail with respect of FIG. 1thereof, an exhaust seal according to the present invention isdesignated generally by numeral 10. The seal 10 is preferably in anendless ring form as shown, and has an inner radial surface 12 and anouter radial surface 14. The surfaces 12 and 14 are formed to sealinglyengage confronting surfaces on pipes and flanges to be joined to oneanother, respectively, an example of such a joint being shown anddescribed later with regard to FIG. 2.

The present exhaust seal 10 is preferably formed of refractory sheetmaterial 16 and knitted wire mesh 18. The refractory material 16 and themesh 18 are preferably pressed together to form the seal 10, it beingdesired and preferred to have the refractory material 16 present on bothof the inner and outer radial surfaces 12 and 14, respectively, as shownin FIG. 1. It is also desired and preferred that the refractory materialsubstantially fill the openings in the mesh 18 and all other air voidswithin the seal 10.

In further detail, a refractory material which is especially suitablefor the seal 10 is graphite in flexible sheet form. For example,automotive grade GTC graphite sheet material as may be obtained fromUnion Carbide Corporation, New York, N.Y., has been found to performsatisfactorily. Of course, other similar or higher grade flexiblegraphite sheet material from other sources may be used as well in thepresent exhaust seal. A preferred thickness range is 0.010 to 0.050inches.

Another refractory material 16 which may be used in the present seal 10is flexible bonded mica sheet. An example of a suitable mica material issilicone bonded mica paper such as No. 22-05-25 obtainable from MidwestMica and Insulation Company, Cleveland, Ohio. Other flexible micamaterial, such as organic bonded mica sheet is also usable in thepresent invention.

The wire mesh 18 is preferably made of steel, but other materials havingcomparable strength and resiliency could be used as well. The mesh wiremay have a diameter in the range of about 0.0035 inches (0.089 mm.) to0.011 inches (0.279 mm.) and the openings between adjacent wires in themesh is preferably in the range of about 0.125 inches (3.18 mm.) to0.250 inches (6.35 mm.).

In accordance with the present invention, and referring to FIGS. 4 and5, exhaust seal 10 is manufactured by convoluting a strip of refractorymaterial 16 with one or more overlying pieces of knitted wire mesh 18 toform a generally cylindrical preform 44. The length of the mesh piece orpieces 18 is arranged to suit the finished size of the seal 10, and itis preferred that the mesh length correspond to two or morecircumferential lengths of the finished seal 10. The width of the mesh18 is also chosen to suit each seal design, this width being preferablyat least two or more times the height of the finished seal.

The refractory sheet material 16 is prepared by cutting it to form astrip of appropriate length and width. The length of strip 16 depends onthe desired dimensions of the finished seal 10, and is preferably equalto or longer than that of the wire mesh 18. In the event refractorystrip 16 is longer than the mesh piece 18, an offset 19 of therefractory strip 16 is arranged to appear at one end of the overlyinglayers as shown in FIG. 4. The width of the strip 16 is preferably equalto that of the wire mesh 18, but it can be slightly narrower or widerthan the mesh 18 depending upon whether or not it is desired to havesome of the mesh 18 present on the end surfaces of the finished seal 10.

The preform 44 is then loaded into a conventional compression die(unshown) which has a cavity shaped substantially the same size as thatof the finished seal 10. The die is designed in such a manner thatcompression force is applied axially to the preform 44. After insertingpreform 44 into the die, an axial load is applied of sufficient force tocause the preform 44 to collapse to the size and shape of the finishedseal 10.

During the pressing operation, the refractory sheet and the wire meshbecome firmly interlocked to provide a high degree of mechanicalstability and structural integrity to the seal 10.

An exhaust seal including flexible graphite sheet, having a finishedheight of about 0.5 inches (1.27 cm.) and an inner diameter of about 2.0inches (5.08 cm.) as represented by FIG. 1 can be manufactured asfollows.

A double layer strip of knitted steel wire mesh, about 15.75 inches(40.005 cm.) in length and 2.125 inches (5.398 cm.) in width is preparedby flattening and cutting a wire mesh sleeve. The diameter of the meshwire is preferably about 0.011 inches (0.279 mm.). The openings betweenadjacent mesh wires preferably extend from about 0.125 inches (3.18 mm.)to 0.250 inches (6.35 mm.). The prepared strip of wire mesh is thendegreased as by dipping in a solution or by other conventional means.

A 0.015 inch thick flexible graphite sheet, such as GTC automotive gradeas may be obtained from Union Carbide Corporation, New York, N.Y., isprepared by cutting it to form a strip measuring about 24.500 inches(62.23 cm.) in length by about 2.188 inches (5.56 cm.) wide.

The degreased steel mesh strip 18 (FIG. 4) is laid over the preparedgraphite sheet strip 16 so that one end of the mesh 18 coincides with acorresponding end of the graphite strip 16 (these ends not appearing inFIG. 4). The layers thus oriented are preferably fastened together atseveral locations as by staples, so that they are retained in theabovedefined relationship with respect to one another. It will beunderstood that one end of the graphite sheet 16 will be offset, as at19, from the end of the mesh 18 as shown in FIG. 4.

The fastened layers 16, 18 are wrapped about a cylindrical mandril,beginning with the offset end 19 of graphite sheet material 16, andcontinuing with the wire mesh layer 18 facing towards the mandril(unshown) during the wrapping step. When wrapping is completed, preform44 (FIG. 5) is thereby formed. Preform 44 is itself preferably stapledthrough all of its layers or otherwise conventionally secured to retainits shape. For example, an end of preform 44 may be partially removedfrom the mandril and stapled through the removed end, and thereaftercompletely removed and stapled through its other end.

The preform 44 is then loaded into a suitable hand die and axiallycompressed, preferably with a 50 to 75 ton load. The finished seal isthen removed upon disassembly of the die.

An exhaust seal according to the present invention, as represented byFIG. 1, including a mica sheet refractory material can be manufacturedin a manner similar to that used to produce the graphite laminate sealas described above. For example, a mica laminate seal, having a finishedinner diameter of about 2.0 inches (5.08 cm.) and a height of about 0.67inches (1.70 cm.) is manufactured as follows.

A double layer strip of knitted stainless steel wire mesh, about 22.500inches (57.15 cm.) long by 2.75 inches (6.985 cm.) wide is prepared byflattening and cutting a wire mesh sleeve of type 309 stainless steelwire. The wire diameter is preferably 0.011 inches (0.279 mm.). Theopenings between adjacent mesh wires preferably extend from about 0.125inches (3.18 mm.) to 0.250 inches (6.35 mm.). The prepared mesh strip isthen conventionally degreased.

A silicone bonded mica paper, such as No. 22-05-25 obtainable fromMidwest Mica and Insulation Company, Cleveland, Ohio, is prepared bycutting it in the form of a strip having a length of about 30 inches(76.2 cm.) and a width of about 2.875 inches (7.30 cm.).

The prepared wire mesh is then overlaid on the mica paper strip so thatone end of the paper extends out from a corresponding end of the mesh bya distance of about 6.625 inches (16.828 cm.). The two layers are thenstapled together, preferably at two locations near the offset end.

The stapled layers are then wrapped around a cylindrical mandril,beginning with the offset end of the mica sheet, the wire mesh facingtowards the mandril during this wrapping step. When wrapping iscompleted to define a preform, the preform is retained in shape as by arubber band secured therearound. The preform is then removed from themandril and loaded into a suitable die which has preferably been sprayedwith a standard dry-type silicone mold release. Finally, the preform isaxially compressed under a load of approximately 50 to 75 tons. Aftercompression is relaxed, the finished seal is mechanically ejected fromthe die.

Both of the seals produced as described above exhibit unusual resiliencycharacteristics and a degree of lubricity on their bearing surfacesmaking them especially well suited for tolerating rotative pipe movementon their bearing surfaces.

Referring to FIG. 2, the seal 10 of the present invention is shownpositioned in a "ball and socket" type joint of the kind intended foruse in exhaust systems of transversely mounted automobile engines. Thejoint is made between confronting ends of pipes 20 and 22, the pipe 20defining a port for an exhaust manifold (unshown) and the pipe 22 beingan automobile exhaust tail pipe which is usually secured underneath theauto as by unshown flexible clamping means.

It will be understood that during engine operation, the pipe 20 willundergo rotative movement relative to tail pipe 22 such as describedearlier. Seal 10 is strong enough to withstand the stresses produced byrelative movement while providing a seal which prevents exhaust gasleakage.

In the typical joint configuration of FIGS. 2 and 3, the exhaustmanifold pipe 20 has a flange 24 securely joined thereto in the vicinityof its open end as by weld 26, for example. A portion 28 of pipe 20 isallowed to extend forwardly of flange 24 for a distance sufficient toallow the seal 10 to be inserted thereover, as shown in FIG. 2. It willbe appreciated that the inner radial surface 12 of the seal 10 ispreferably in substantial contacting relationship with the outer surfaceof the forward pipe portion 28, thereby requiring that the innerdiameter of the seal 10 be substantially equal to the outside diameterof the exhaust manifold pipe 20.

Exhaust tail pipe 22 has a flange 30 securely joined thereto near itsopen end, the flange 30 being welded at 32 to pipe 22, for example.Extending forwardly of flange 30 is an outwardly flared section 34 oftail pipe 22, the inside surface of the flared section 34 beingpreferably arcuately formed as is the outer bearing surface 14 of seal10, so that the seal bearing surface 14 defines the "ball" and theflared section inside surface forms the "socket" of the joint. Thesection 34 may also be conically tapered so as to maintain a linecontact seal against the outer seal surface 14. The seal of the presentinvention will therefore perform satisfactorily when bearing against aconically tapered pipe surface, as well as against a complimentarilyshaped arcuate pipe surface as shown in FIG. 2.

The opening defined by flared portion 34 is of an extent sufficient tooverextend the forward pipe portion 28, thereby permitting the presentseal 10 to be disposed between the confronting ends of the pipes 20 and22, respectively. It will be appreciated that the seal 10 is mounted tosealingly engage the outer surface of forward pipe portion 28 and theinner surface of the flared portion 34 when these pipe portions areurged towards one another as explained below.

A pair of bolts 36 extend through corresponding openings 38 in flange30. Significantly, the openings 38 are slotted as shown in FIG. 3 so asto provide for rocking movement of the bolts 36, this movement beingcaused by the movement of manifold pipe 20 during engine operation.Bolts 36 theadingly engage corresponding threaded openings 40 providedthrough flange 24 on manifold pipe 20. It will therefore be understoodthat as the manifold pipe 20 is caused to rotate relative to tail pipe22, the bolts 36 will be free to rock back and forth within the slots38.

The bolts 36 urge the flange 30 towards flange 24 by way of compressionsprings 42 disposed between the heads of bolts 36 and the opposedsurface of flange 30. It will be apparent that the above-mentionedsidewise movement of bolts 36 will not be appreciably restrained by thesprings 42 when using the configuration of FIGS. 2 and 3.

With the seal 10 in the position shown in FIG. 2, it will also beapparent that it is restrained from relative axial movement due to itsabutment on one side against the flange 24, and the abutment of itsouter radial bearing surface 14 in sealing relationship with the insideof the flared pipe portion 34. However, the seal 10 tolerates relativerotative movement between the confronting surfaces of the pipes 20 and22 as by permitting movement of the tail pipe flared portion 34 over itsbearing surface 14. Seal 10 can also absorb an unusually high degree ofstress resulting from such movement, and still maintain an effectiveseal.

While the foregoing description has been primarily directed toapplications of the seal 10 in which relative rotative movement andstress must be tolerated by the seal during operating conditions, itwill be understood that the seal of the present invention may beeffectively used in other applications, not only in the automotivefield, but in many others, such as marine and aviations, for example.

Modifications and variations of the present seal and its method ofmanufacture will be apparent to one skilled in the art. It is thereforeintended that all such equivalent methods and materials be includedwithin the scope of the appended claims which define the presentinvention.

What is claimed is:
 1. A method of producing a substantially coherenthigh temperature composite seal comprising the steps of constructing apreform comprising flexible refractory sheet material aligned againstflexible knitted wire mesh by convoluting of strip of refractorymaterial with one or more overlying pieces of knitted wire mesh to forma generally cylindrical preform, said wire mesh being formed of wire andhaving voids of given size between said wires, disposing said preform ina compression die, said die having a cavity size and shape which issubstantially the same as the desired composite seal, and applying anaxial load to said preform, said load being of sufficient force tocollapse said preform to substantially the size and shape of saidcomposite seal and to cause said refractory material to substantiallyfill the openings in said wire mesh and to become firmly interlockedwith said mesh.
 2. The method of claim 1 wherein said axial load issufficient to cause the refractory material to substantially fill allair voids in said composite seal.
 3. The method of claim 1 wherein saidseal is an endless ring.
 4. The method of claim 3 wherein said seal isin the form of an exhaust seal comprising inner and outer radialsurfaces adapted to engage surfaces on pipes and flanges to be joined toone another.
 5. The method of claim 1, wherein the length of wire meshcorresponds to two or more circumferential lengths of the finished seal.6. The method of claim 1 wherein the width of said mesh is two or moretimes the height of said finished seal.
 7. The method of claim 1 whereinsaid refractory sheet material is graphite.
 8. The method of claim 1wherein said refractory sheet material is mica.
 9. A method of producinga substantially coherent high temperature exhaust seal adapted tosealingly engage confronting surfaces on pipes and flanges to be joinedto one another to form a flexible joint comprising the steps ofconstructing a preform by convoluting a strip of flexible refractorysheet material with one or more overlying pieces of flexible knittedwire mesh, said wire mesh being formed of wire and having voids of givensize between said wires, disposing said preform in a compression die,said die having a cavity size and shape which is substantially the sameas the desired exhaust seal, and applying an axial load to said preform,said load being of sufficient force to collapse said preform tosubstantially the size and shape of said exhaust seal and to cause saidrefractory material to substantially fill the openings in said wire meshand substantially all other air voids within said exhaust seal and tobecome firmly interlocked with said wire mesh.